It's also a product that enhanced the media it was in, which was a pretty poor stoner flick otherwise. If it hadn't featured White Castle (or starred two non-white actors in the leads, but that's another topic...) it never would have done as well as it did. I'm fairly certain it stops being product placement what the product is actually more loved than the feature shilling it.
I don't know. When I saw the movie, I lived in California. Over there we don't even have White Castle. All my friends never even heard of White Castle, and I only knew the name from someone mentioning it in passing. We still all loved the movie regardless of the fact it was White Castle. Whether it would have done better with McDonalds or KFC, I don't know, and really, neither can you.
White Castle didn't comission that movie;
No brand company ever "commissions' a movie, otherwise it would just be a commercial. Product placement happens when a production company goes to another company and basically says "Hey, we want to have you in our movie, what will you give us for promoting you?" The company then does one of a few things. (or all of the things)
A) They send a nice check for having the main character drop that "he wants a coke" while walking up to a coke machine, or pulls out some slick shoes and has to put them on going "Oh yeah".
B) Supplies them with needed items that are required for filming, like how Michael Bay got all 69 with GM so that he could have all his cars he needed for filming Transformers.
C) Supplies them with locations and approvals to film at those locations. For instance, the White Castle in Harold and Kumar.
In the end, it's all about advertising, it is all product placement. The only time you can say product placement never happens in a movie, is if you never talk about, show, or use any actual brand product at any point in the movie. That goes the same for written names, logos, etc...
We were taught in film school to actually set scenes to make sure certain products were not even visible for legal reason, like Coca-Cola can actually get on your ass if they don't approve of you using the coke machine in a movie, and Mercedes even has stipulations that they will not allow one of their cars to be used in a movie crash in which someone dies. All brands need the consent of the company that owns them.
And that is my insider film lesson of the day.
